Heat exchangers such as, for example, corrugated plate-type exchangers, shell and tube-type exchangers, tube and fin-type exchangers, and other types of heat exchangers known in the art are used to transfer thermal energy between two fluids without direct contact between the two fluids. In particular, a primary fluid is typically directed through a fluid passageway of the heat exchanger, while a cooling or heating fluid is brought into external contact with the fluid passageway. In this manner, heat may be conducted through walls of the fluid passageway to thereby transfer energy between the two fluids. One typical application of a heat exchanger is related to an engine and involves the cooling of air drawn into the engine and/or exhausted from the engine.
As engine manufacturers are continually urged to increase fuel economy, meet lower emission regulations, and provide greater power densities, the pressure and temperature differentials across the heat exchangers are increasing. In addition, due, at least in part, to the increasing pressure and/or temperature differentials found in today's heat exchangers, acidic condensation on and corrosion of the exchanger's fluid passageways are also increasing. As a result, today's heat exchangers are either unable to withstand the extreme conditions or are fabricated from exotic alloys that can withstand the pressure, temperature, and acidic extremes. Subsequently, the heat exchangers either fail, or are so heavy, expensive, and difficult to manufacture that they become impractical for most applications.
One solution to the above-described problems may include the use of a multi-material heat exchanger. One such heat exchanger is described in U.S. Pat. No. 3,880,232 (the '232 patent), issued to Parker on Apr. 29, 1975. In particular, the '232 patent discloses a counter-flow recuperative heat exchanger in which the material composition of the fins and plates within the exchanger vary in the flow direction according to temperature and stress conditions. Specifically, a first plate of high stress- and heat-resistance quality material, such as Inconel, is welded edgewise to a second plate of lower stress- and heat-resistance quality material, such as SAE 1020 steel, which in turn may be edge-welded to another plate of still lesser quality material. A plurality of such elements formed as plates and fins are then fabricated into a unitary heat exchanger core and arranged in a position whereby the sections of the elements having the high stress and heat-resistance qualities are at the higher temperature end of the heat exchanger. By utilizing multiple materials of differing stress and heat-resistance qualities, a lower cost yet durable exchanger may be fabricated.
Although the heat exchanger of the '232 patent may be low cost, as compared to an all-Inconel heat exchanger, and have greater heat-resistance, as compared to an all-steel (SAE 1020 steel) heat exchanger, its applicability may be limited. Specifically, the heat exchanger of the '232 patent may only be beneficial where high temperatures are problematic. In situations where cooler temperatures result in acidic condensation on the passageways of the exchanger, the multi-material heat exchanger of the '232 patent may provide little improvement, if any, over a single material heat exchanger.
The disclosed heat exchanger is directed to overcoming one or more of the problems set forth above.